Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.47   3.273%   $146.1003   $146.10   $146.10   $146.10  
  Purchase #2 $220.95   5.419%   $232.9233   $232.92   $232.90   $232.90  
  Purchase #3 $95.42   4.823%   $100.0221   $100.02   $100.00   $100.00  
  Purchase #4 $245.76   7.266%   $263.6169   $263.62   $263.60   $263.60  
  Purchase #5 $110.35   7.571%   $118.7046   $118.70   $118.70   $118.70  
  Purchase #6 $63.76   8.354%   $69.0865   $69.09   $69.10   $69.10  
  Purchase #7 $24.44   12.526%   $27.5014   $27.50   $27.50   $27.50  
  7 purchase totals = $902.15       $957.9551   $957.95   $957.90   $957.90